Field of the Invention
The present invention relates to a backlight unit and a display device and, more particularly, to a backlight unit, which is structured to have no light guide plate, and a display device including the backlight unit.
Description of the Background Art
Development of information-oriented societies has increased various types of demands for display devices for displaying images, and various display devices have recently been utilized, such as an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), and an OLED (Organic Light Emitting Diode) display.
Among such display devices, the LCD generally includes an array substrate including a thin-film transistor, which is a switching element for on/off control of each pixel area; an upper substrate including a color filter and/or a black matrix; a display panel including a liquid crystal material layer formed therebetween; a driving unit for controlling the thin-film transistor; and a back light unit (BLU) for providing light to the display panel, wherein the state of arrangement of a liquid crystal layer is adjusted according to an electric field applied between a pixel (PXL) electrode provided in the pixel area and a common voltage (Vcom) electrode, and the transmittance of light is adjusted accordingly, thereby displaying images.
Such a liquid crystal display device includes a backlight unit for providing the display panel with light, and backlight units are classified into edge types and direct types according to the arrangement of light sources and the type of transfer of light.
The edge-type backlight unit may include a light source module or a light source device, which includes a light source such as an LED, a holder or a housing for fixing the light source, a light source driving circuit, and the like, and which is arranged on one side of a display device; a light guide plate (LGP) for diffusing light throughout the entire panel area; a reflecting plate for reflecting light towards the display panel; and at least one optical sheet arranged on the upper portion of the light guide plate for the purpose of improvement of luminance, diffusion of light, and protection.
Among the components that constitute the edge-type backlight unit, the light guide plate (LGP) is a plate-shaped member for uniformly guiding light, which is from the light source, throughout the entire display device, and may have a predetermined pattern formed on at least one surface of the plate-shaped member, for the purpose of uniform distribution of light and the like.
Such a light guide plate is made of a light-transmitting plastic material, such as polymethyl methacrylate (PMMA), and thus has a high degree of light transmittance. However, the fact that the light guide plate needs to have at least a predetermined thickness, in order to maintain constant rigidity and the like, has become an obstacle to the slimness of the entire display device.
Furthermore, the light guide plate made of a plastic material has a problem in that, due to the large thermal expansion ratio and the high degree of moisture swelling, there is a restriction on the arrangement in connection with the light source portion, and an additional support structure is needed.
On the other hand, the direct-type backlight unit has a problem in that, although no light guide plate is used, a light-diffusing lens needs to be used for the light source portion, and the fact that a constant optical gap needs to be maintained between the light source portion and the diffuser plate becomes an obstacle to the slimness of the display device.
Therefore, a scheme to replace the light guide plate of the edge-type backlight unit may be required.